The marking of mediums reflects the content of the medium and allows the dissemination of information wherein the end user can identify the subject matter located within the medium. In addition, logos, trademarks, text, graphics, and bar codes can be added to the medium for marketing, sales and cataloging of information.
The printing processes for printing information and graphics on the surface of a medium including plastic disks or compact disks, generally include a silk screening printing process, a printer utilizing ink jet printing technology, a labeling process or a thermal printing process. However, in any printing process, it is desirable that the pressure against the medium be uniformly applied during the printing process in order to insure the highest quality of printing onto the medium.
One of the most popular types of media are optical disks, such as compact disks and digital video disks, or digital versatile disks. The optical disk or CD has recently become a popular form of media for storing digital information, recording high quality audio and video information and also for recording computer software of various types. With advances in technology, it is now possible not only to read information from such optical media, but also to record digital information directly onto the media. For example, recordable compact disks (referred to as CD-Rs) may have digital information recorded on them by placing the CD-R into a compact disk recorder that receives the digital information from a computer. Such forms of optical media are thus particularly useful for data distribution and/or archiving.
Compact disks are standardized in two sizes and configurations, one having an overall diameter of 4.72 inches, a central hole of 0.59 inches, and a central region about the center hole of 1.50 inches in diameter, wherein no information is either printed or recorded. The other standard disk size is 3.5 inches in overall diameter, with a comparable central hole size and central region. In the case of disks for utilization in connection with computer processors, the recording formats and content are typically adapted to the particular generalized type of computer processor with which the disk is to operate. Some compact disks are recorded in such a way as to be usable with several different computer processor types, i.e., PC, Macintosh, etc.
The significant increases in use of CD disks and CD-R disks as a data distribution vehicle has increased the need to provide customized CD label content to reflect the data content of the disk. Initially, the customized label information was “hand written” on the disk surface using felt tipped markers. While this approach permitted users to individually identify disks, it tends to be labor intensive, prone to human error in transcription, and aesthetically limited.
Other attempts to provide a CD or CD-R labeling solution have incorporated digitally printed adhesive labels. Precut labels are printed using desktop or commercial ink-jet, thermal wax transfer, or printers. An example of such labels is the STOMP Company's (Irvine, Calif.) CD Stomper package of die cut CD labels that can be printed on any 8.5 by 11 inch ink jet or laser electrophotographic printer. Following printing, the labels can be applied manually with or without the aid of an alignment tool or a specially designed machine. This method can be labor intensive, and the CD-R can be damaged if the label is removed. In addition, system performance problems can occur due to disk imbalance or label de-lamination in the CD writer or reader.
Within the past several years, however, methods for direct CD labeling have been growing in prominence. These methods utilize the versatility and ease of the setup associated with digital printing to provide customized label content directly on a disk surface. The most commonly used direct CD printers incorporate ink jet or thermal wax transfer technologies. These printers can be either stand alone or integrated into a computerized disk writing system reducing problems associated with labor, human error, disk damage, and imbalance.
CDs are often coated with a printable surface opposite to the surface from which the information is recorded and retrieved. On the printable surface, a label is printed which can be logos, trademarks, text, graphics, and bar codes, etc., which are related to the information stored on the CD. The label also protects the CD from physical damage. Because the CD spins at high speed in the writer and the player, the CD labels needs to be precisely balanced to the center of the disk for smooth rotation.
Labeling of CD disks has routinely been accomplished through screen-printing methods. While this method can provide a wide variety of label content, it tends to be cost ineffective for run lengths less than 300-400 disks because the fixed cost on unique materials and set-up are shared by all the disks in each run. The screen printing technique is well described in the textbook “Graphic Arts Manual”, edited by Janet and Irving Field, Arno/Musarts Press, New York, N.Y., 1980, pp. 416 to 418. In screen printing a stencil of the image is prepared, placed in contact with the CD and then ink is spread by squeegee across the stencil surface. Where there are openings in the stencil the ink passes through to the surface of the CD, thus producing the image. Preparation of the stencil is an elaborate, time consuming and expensive process.
However, since compact disks are an inexpensive medium for storing digital information that may relate to audio, video and/or any type of information or data that is conveniently stored in digital form that in order to appropriately label such media with regard to the content that is recorded on the disk, programmable disk printers, such as ink jet printers and thermal transfer printers have been devised. These printers print the surface of the disk with graphics and other information that can be customized to correspond to the information recorded on the disk by the CD-R recorder.
An advantage of thermal transfer printers is the ability of the print engine to print with greater speed than a typical ink jet printer or labeling process. In addition, a thermal printer can print on disks prepared with an inexpensive lacquer coating. A typical thermal transfer printer includes a print head that applies a contact pressure to the media to be printed.
One type of thermal transfer printer will typically consist of a mechanism that has a stationary print head, a ribbon, and assembly that moves the media under the print head. The print head contains an array of heating elements. The ribbon is a plastic film with a wax or resin compound deposited on one side. The print head is in contact with the ribbon during printing, and the ribbon is in contact with the media.
By heating the areas of the ribbon, the wax or resin compound is deposited on the media. Printing occurs by moving ribbon and the media at the same rate across the print head, while firing the heating elements in a desired pattern. The print head must exert some pressure on the media for successful transfer of the wax or resin to the media.
A second type of thermal printer is a direct transfer printer, which uses thermally sensitive media that changes color when heated, therefore a ribbon is not required. With thermally sensitive media, the print head marks the media by generating a pattern of heated and non-heated areas on the surface of the media, as it moves under the print head.
Thermal transfer printers require the print head to contact the printable surface at a uniform pressure for optimum transfer of a marking medium from a ribbon to the media (or heat in the case of direct thermal transfer printer). However, any variation in print head pressure to the media can result in improper printing on media such as non-printed areas or uneven print density.
Printing on rectangular objects, such as a piece of paper, is relatively straight forward, since the print head pressure remains constant during the entire printing process. The pressure remains constant because the area of contact between the print head and the media does not change. For example, in printing a 5″ wide piece of paper the print head is always in contact with 5″ of media. In contrast, printing on a 5″ diameter disk, the area of contact would initially be very small as the print head is at the edge of the disk, but then increases to 5″ as the print head crosses the center of the disk. After crossing the center of the disk, the area of contact decreases as the print head travels the far edge of the disk.
When the force of the print head applied to the media is constant and the print head travels across a rectangular shaped media, the pressure per unit area is constant. If the print head travels across a disk shaped media, the print head pressure to the media will change as the print head travels across the disk. When the force of the print head applied to the media is constant and the print head travels across a disk shaped media the pressure per unit area changes as the contact area increases and decreases.
Thermal transfer printer generally includes any transfer of an imaging compound, such as a wax, wax resin or wax resin composite, or a dye from a carrier ribbon, film or web to a substrate, as shown, a disc shaped substrate such as a compact disc (CD) or digital versatile disc (DVD). The velocity of movement of the compact disc is varied along with a platen position and engagement force to efficiently use available power so as to compensate for the changing power required by the print head for printing differing print line lengths and also space the print head from raised rims around the central opening of DVD'S.
Typically, the technology for printing onto CDs utilizes expensive head actuating and force modifying mechanisms. The print head is moved on pivotally mounted arms that extend substantially beyond the envelope of the print head, with a linearly driven carriage that has to hold the disk over a flat resilient surface with a clamping device that moves with the carriage. In addition, the threading of the print ribbon through the print head and mounting ports can be of the presently available printers can be difficult and includes taping the ribbon to the carriage, then taping the ribbon after the carriage is driven into the printer. This leads to large, high-cost thermal transfer CD, CD-R and DVD printers. It is desirable to substantially reduce the size in order to take less space for the CD printers, as well as manufacturing costs and user interaction.
Conventional techniques for thermal printing onto circular objects, such as a CD disc, cause the circular object to be printed to pass beneath a thermally activated print head at a uniform rate of speed. It can be appreciated that by varying the speed at which the circular object passes beneath the print head to manage the power needed for the printing process and varies the force on and position of the disk as a function of the position of the disk under the print head. This permits the printer to utilize a non-dedicated and limited power source, such as a personal computer power supply and also to reliably print on DVDs which have a raised rim around the center portion of the disc.
Typically, the ink jet label printing requires a hydroscopic coating on the CD surface for accepting aqueous ink solutions. The thermal wax transfer can print on a lacquer (shiny), matte, or silk-screened disc surface. Both printing techniques, though, are bi-model in nature and are therefore not suitable for printing continues tone photographic images.
Many users want to print photographs on the labeling surface of the CDs. This is especially desired for photo CDs, where thumbnail images can be printed on the label as an index of the images stored in the CD. A photographic image is best printed with a continuous-tone printer, rather than bi-model printer such as ink jet or thermal wax transfer printers.
Accordingly, what is desired is an in-line marking system comprising a thermal printer, which marks indicia on the disk in an efficient and expedient manner.